Mixed oxide fuel pellets of fuel rods of nuclear reactor cores are likely to be fabricated so that the plutonium oxide portion of the fuel is distributed throughout the entire pellet, including locations near the outer surface thereof. Large agglomerates of PuO.sub.2 in the vicinity of the outer surface of the fuel pellet near the cladding of the fuel rod will cause local power spikes and this oftentimes results in local hot spots in the cladding. Of greater concern is the fact that large PuO.sub.2 agglomerates will have a deleterious effect on cladding integrity during a severe power transient. The results obtained to date indicate that non-homogeneous mixed-oxide fuel rods can fail by a localized melting and perforation of the cladding of the fuel rod, followed by expultion of PuO.sub.2 particles into the coolant. Such a response is clearly undesirable because the limiting design base accident for power reactors is established on the basis of maintaining cladding and fuel integrity during a power transient.
In view of the foregoing problems, a need exists to provide a fuel rod whose mixed-oxide fuel pellets do not cause a breakdown in the structural integrity of the fuel rod itself, yet assures that the fuel pellets in the rod are fabricated to meet rigid standards of PuO.sub.2 particle homogeneity. Alternatively, a need exists for a fuel pellet that would intrinsically preclude the formation of large PuO.sub.2 agglomerates in the outer region of the fuel pellet where such agglomerates have the greatest potential for deleterious effects during transient operation.
Prior art relating to this problem includes the following references:
1. Regulatory Staff, USAEC, Technical Report on Effects of Plutonium Utilization on the Performance of Light Water Reactors, WASH 1303, April 1974.
2. M. D. Freshley, et al, Behavior of Discrete Plutonium Dioxide Particles in Mixed-Oxide Fuel During Rapid Power Transients, Nucl. Tech., 15, 239 (1972).